Piston size for 951 engine

[sirgmfk]

Hello. I start rebuild top end 951. The cylinders measure 89mm. What pistons size should i use for 89mm bore? Should i go with 89mm pistons kit or go over to 89.5mm or go under 88.75? Another question should i Nikasil plate cylinders or its ok to use like this after hone?

 

[themk]

I'll let the true 947 experts weigh in, but it sounds like it's already bored over +1mm. You could go to 89.5 and bore the cylinder sleeves +1.5 over stock, but really you're looking into re-sleeve territory. Going under is not an option, however if you got a new cylinder sleeve you could go all the way back to stock (88mm). Note that the RAVE valves have to be trimmed/clearanced for the oversized pistons.

EDITED TO ADD:
Typically the 947 crank doesn't last much longer than a new top end does. I'd look at doing a complete rebuild (incl crank/bottom end) rather than just a top end job. You have been warned haha.

 

[mikidymac]

No, you don’t plate these cylinders.

Your machine shop will tell you what size pistons are needed.